A corner where three edges meet is also called a vertex. A vertex can be also used in Algebra 2, in Quadratic Equations.
A vertex can be the corner of a polyhedron in which case at least three edges meet at a vertex.
It is the vertex and its plural is vertices
That's a "vertex".
Vertex mate :) 3 or more is a vertex
Yes, you need at least two edges to make a corner. For example, in a cube, the vertex is formed because three edges meet. In a regular square, each side meets to make a corner. If you had only one edge(corner)then it would just go on and on, and since there's not another edge to meet it, it would never make a corner anyway.